LDO With Improved Common Gate Class-AB OTA Handles any Load Capacitors and Provides Fast Response to Load Transients
Cristian Răducan, Alina-Teodora Grãjdeanu, Cosmin-Sorin Pleșa, Marius Neag, Andrei Negoiță, Marina Ţopa
Abstract
This article proposes an LDO with fast response to load transients that can handle any practical capacitive loads. These features are mainly due to a novel frequency compensation circuit tailored for its error amplifier, which is based on an improved version of the popular common gate amplifier. A simple yet effective approach to the small-signal analysis of LDO with multiple feedback loops is employed to analyse intuitively the LDO and derive key design constraints. Simulation and measurement results performed on a test chip implemented in standard 130nm CMOS process validated the proposed LDO. It requires only 0.7μA quiescent current but exhibits an excellent response to load transients: when the load current jumps from 0A to 100mA in 1μs the output voltage presents an undershoot of 76mV and an overshoot of 198mV, without decoupling capacitors. It compares well against seven LDOs designed with common gate error amplifiers for similar levels of supply voltage, output voltage and current and against seven fast LDOs employing different error amplifiers. A figureof-merit that considers the quiescent current, the maximum load current and capacitance, as well as the output voltage deviation, yielded a value for our LDO 39.8 times better than for the nearer competitor that employs common gate amplifier and 6 times better than the one employing a different error amplifier. When considering edge time and process scaling the performance of the proposed LDO is 4.8, respectively 4.5, times better than the second best in both comparisons.